Accuracy of Hadlock1 and Shepard Equation in Prediction of Intrauterine Fetal Weight

Abstract

Background : Fetal weight prediction is very importance and will give benefit to both mother and fetus. Because both will get good support appropriately and timely. It will also give information to obstetrician to help making decision so to select the most accurate equation is very crucial.

Objective : To develop the predictive intrauterine fetal weight equation by using real time ultrasound to measure fetal abdominal circumference  and femur length.

Methods : A prospective study was conducted during July15,2007 to December20,2007 in 133 pregnant women in the labour room of Nong Khai Hospital. Data analysis  for frequency, percentage, mean, standard deviation, comparison of the accuracy between the two equations using odd ratio and regression analysis were used to bring up the new equation.

Results : 136 fetuses were included in the study. Hadlock1 equation had more accuracy in weight prediction when compared with Shepard equation. However, the accuracy of predicted value within 10% of actual birth weight was only  about 69.1% . So the new predictive intrauterine fetal weight equation was

weight(gm)   =  weight calculate by Hadlock1equation x 0.932+ 316.66

R = 0.891   and  adjusted R²  = 0.792.

Conclusion : The new predictive intrauterine fetal weight equation using real time ultrasound to measure fetal abdominal circumference and femur length had high accuracy for prediction of intrauterine fetal weight. It has more accuracy than Hadlock1 and Shepard equation. However, this new equation must be incorporated with each evaluation when determining this condition. Though this is a recommended equation, further adjustment through evaluation may be required.

Keywords :  prediction, fetal weight, femur length, abdominal circumference, ultrasound